The present invention relates to process tools for the fabrication of integrated circuits on semiconductor wafer substrates. More particularly, the present invention relates to a tool for measuring the pressure difference between atmospheric or ambient air in a semiconductor fabrication facility and an indexer in a process tool to prevent influx of potential wafer-contaminating particles into the indexer.
Generally, the process for manufacturing integrated circuits on a silicon wafer substrate typically involves deposition of a thin dielectric or conductive film on the wafer using oxidation or any of a variety of chemical vapor deposition processes; formation of a circuit pattern on a layer of photoresist material by photolithography; placing a photoresist mask layer corresponding to the circuit pattern on the wafer; etching of the circuit pattern in the conductive layer on the wafer; and stripping of the photoresist mask layer from the wafer. Each of these steps, particularly the photoresist stripping step, provides abundant opportunity for organic, metal and other potential circuit-contaminating particles to accumulate on the wafer surface.
In the semiconductor fabrication industry, minimization of particle contamination on semiconductor wafers increases in importance as the integrated circuit devices on the wafers decrease in size. With the reduced size of the devices, a contaminant having a particular size occupies a relatively larger percentage of the available space for circuit elements on the wafer as compared to wafers containing the larger devices of the past. Moreover, the presence of particles in the integrated circuits compromises the functional integrity of the devices in the finished electronic product. When the circuits on a wafer are submicron in size, the smallest quantity of contaminants can significantly reduce the yield of the wafers. For instance, the presence of particles during deposition or etching of thin films can cause voids, dislocations, or short-circuits which adversely affect performance and reliability of the devices constructed with the circuits. Accordingly, technological advances in recent years in the increasing miniaturization of semiconductor circuits necessitate correspondingly stringent control of impurities and contaminants in the plasma process chamber. Currently, mini-environment based IC manufacturing facilities are equipped to control airborne particles much smaller than 1.0 xcexcm, as surface contamination continues to be of high priority to semiconductor manufacturers. To achieve an ultra-clean wafer surface, particles must be removed from the wafer. Particle-removing and contamination-preventing methods are therefore of utmost importance in the fabrication of semiconductors.
During the photolithography step of semiconductor production, light energy is applied through a reticle mask onto a photoresist material previously deposited on the wafer to define circuit patterns which will be etched in a subsequent processing step to define the circuits on the wafer. Because these circuit patterns on the photoresist represent a two-dimensional configuration of the circuit to be fabricated on the wafer, minimization of particle generation and uniform application of the photoresist material to the wafer are very important. By minimizing or eliminating particle generation during photoresist application, the resolution of the circuit patterns, as well as circuit pattern density, is increased.
Photoresist materials are coated onto the surface of a wafer by dispensing a photoresist fluid typically on the center of the wafer as the wafer rotates at high speeds within a stationary bowl or coater cup. The coater cup catches excess fluids and particles ejected from the rotating wafer during application of the photoresist. The photoresist fluid dispensed onto the center of the wafer is spread outwardly toward the edges of the wafer by surface tension generated by the centrifugal force of the rotating wafer. This facilitates uniform application of the liquid photoresist on the entire surface of the wafer.
Spin coating of photoresist on wafers is carried out in an automated track system using wafer handling equipment which transport the wafers between the various photolithography operation stations, such as vapor prime resist spin coat, develop, baking and chilling stations. Robotic handling of the wafers minimizes particle generation and wafer damage. Automated wafer tracks enable various processing operations to be carried out simultaneously. Two types of automated track systems widely used in the industry are the TEL (Tokyo Electron Limited) track and the SVG (Silicon Valley Group) track.
The various processing steps used in the fabrication of devices on a wafer substrate are carried out sequentially in multiple processing systems. An example of such a processing system is an automated track-type semiconductor fabrication apparatus which may be obtained from the Tokyo Electron Co., of Tokyo, Japan, and is generally indicated by reference numeral 1 in the schematic of FIG. 1. The apparatus 1 includes an enclosure 2 and a track 3 which transports semiconductor wafer substrates 12 (FIG. 2) among multiple process stations where the substrates 12 are subjected to various treatments during the fabrication process. The apparatus 1 includes a spin coater station 4, further shown in FIG. 2, and multiple hot/cold plate stations 5, 6, and 7, respectively, arranged in series. The track 3 transports wafer containers 11, each of which contains multiple wafer substrates 12, from upstream process stations (not shown) to the spin coater station 4, in which a coating layer of photoresist material, for example, is applied to the surface of the substrates 12. Next, the track 3 transports the wafer containers 11 and coated wafer substrates 12 into and out of the hot/cold plate stations 5, 6, 7 for conversion of the spin-coated material coated on the substrates 12 into a low dielectric constant material, according to the knowledge of those skilled in the art.
In typical operation of the apparatus 1, the wafer container 11, which may be a SMIF (standard mechanical interface) pod, for example, contains the multiple wafer substrates 12 and is loaded into an indexer 10 of the spin coater station 4. Each of the wafer substrates 12 is individually transferred from the wafer container 11 and placed on a wafer support 15 in a process chamber 14. During the photoresist coating process, the wafer support 15 is rotated at high speeds as the liquid photoresist (not shown) is dispensed onto the substrate 12 through a dispensing opening (not shown) in the top of the process chamber 14. The photoresist is uniformly distributed on the surface of the rotating substrate 12, after which the coated substrate 12 is transferred back into the wafer container 11. After all of the substrates 12 in the wafer container 11 have undergone the coating process, the wafer container 11, containing the coated substrates 12, is removed from the indexer 10, and the track 3 distributes the wafer container 11 to the next station in the apparatus 1.
During the photoresist application process in the process chamber 14, the high rotational speed of the wafer support 15 generates photoresist powder particles in the process chamber 14. While most of these particles are removed by operation of a vacuum exhaust line (not shown), a small quantity of the particles remain in the process chamber 14. Due to the top dispensing opening (not shown) provided in the top of the process chamber 14, the pressure of air inside the process chamber 14 equalizes with the pressure of ambient or atmospheric air surrounding the process chamber 14. Thus, in the event that the pressure of the air or gas in the indexer 10 is lower than the atmospheric pressure of the air or gas in the process chamber 14, the particles tend to flow with the turbulent gas or air from the higher-pressure process chamber 14 into the lower-pressure indexer 10, as indicated by the arrows in FIG. 2. Consequently, the photoresist particles settle on the substrates 12 in the wafer holder 11 and impart ball-type defects to the devices on the substrate 12, which defects reduce the yield of devices on the substrates 12 and necessitate scrapping of the affected substrates 12. Accordingly, it is very important to monitor the pressure of air or gas in the indexer 10 and maintain this interior pressure at a higher level than the pressure in the process chamber 14, in order to prevent turbulent flow of air or gas from the process chamber 14 into the indexer 10 and attendant contamination of substrates 12 in the wafer holder 11 during transfer of a substrate 12 into the process chamber 14.
An object of the present invention is to provide a device for measuring the pressure of air or gas in an indexer of a process tool for semiconductors.
Another object of the present invention is to provide a device for comparing the pressure of air or gas in an indexer of a process tool to ambient or atmospheric air or gas.
Still another object of the present invention is to provide a device for reducing or preventing contamination of devices on a WIP (work in progress) wafer substrate.
Yet another object of the present invention is to provide a device for preventing unnecessary scrapping of semiconductor wafer substrates due to powder contamination of the substrates.
A still further object of the present invention is to provide a device which is suitable for comparing atmospheric or ambient air pressure with the interior pressure of an indexer in a variety of processing tools for semiconductors.
Yet another object of the present invention is to provide a device which is capable of comparing atmospheric pressure of air inside a spin coating chamber with pressure of gas or air inside an indexer for indexing and loading substrates into the chamber.
In accordance with these and other objects and advantages, the present invention is generally directed to a device for measuring or comparing the difference between the pressure of air or gas in an indexer for a process tool with the pressure of atmospheric or ambient air surrounding the process tool, in order to prevent flow of air and potential device-contaminating particles from the process tool chamber into the indexer. The device of the present invention comprises a wafer container having a pressure difference meter provided in fluid communication therewith. In use, the wafer container is placed in the indexer of the process tool, which is operated according to normal operational parameters. The pressure difference meter measures the difference in pressure between the air in the indexer, which equalizes with pressure in the wafer container, and the ambient or atmospheric air surrounding the chamber, which equalizes with the pressure of the air in the process chamber. The air pressure in the indexer can then be adjusted to a value higher than the ambient or atmospheric air pressure to prevent influx of air and particles from the process chamber into the indexer and wafer container.